This research will develop multivalency as a strategy for modulating biological interactions. Multivalent interactions are those that involve multiple receptors interacting simultaneously with multiple ligands. Multivalent interactions are ubiquitous in biology-in infectious disease, in processes involving antibodies, in blood clotting, metathesis, platelet activation, and inflammation, and in many conditions in which cells interact with surfaces-but are seldom explicitly the target of study or of therapy. Drugs are designed primarily on the principle of "one drug, one receptor". The objective of this research is to explore a range of multivalent interactions using multivalent ligands as probes, to understand those types of biologically relevant interactions that are most easily controlled by synthetic, multivalent entities, and to demonstrate proof-of-concept in the use of multivalent species as drugs. Test systems will be drawn primarily from infectious disease: E. coli, pseudomonas, B. anthracis, and influenza are of particular interest. It will also develop new analytical systems that are tailored to the special requirements of multivalency.